Solar panels are being installed on the White House this week while the Obamas are away on vacation, three years after the administration first vowed to do so.

"The White House has begun installing American-made solar panels on the first family's residence as part of an energy retrofit that will improve the overall energy efficiency of the building," according to a White House official.

In addition to the solar panels, energy-saving equipment such as updated building controls and variable-speed fans are also being installed at 1600 Pennsylvania Avenue.

The retrofit is three years in the making. The White House first announced in October 2010 that it planned to install solar panels on the roof. "As we move towards a clean energy economy, the White House will lead by example," then-Secretary of Energy Steven Chu said at the time.

Why the delay?

"The White House isn't your typical home," a White House official explained. "It has very specific requirements that had to be addressed as a part of the energy retrofit. This includes taking the time to update the technical scope of the retrofit project to include energy efficiency improvements."

This is not the first time solar panels have been installed at the White House.

In June of 1979 President Jimmy Carter, an early advocate of the energy-saving technology, installed 32 solar panels on the White House roof. The largely symbolic panels, which were used to heat water in the White House staff kitchen, were removed in 1986 during roof repairs made under the Reagan administration.

In 2003, President George W. Bush quietly installed a small solar system on the White House grounds, including panels on the pool cabana to help with water heating.